This invention relates to a cooling system for an electromechanical rotary machine.
Electromechanical rotary machines, such as electric motors or generators, may generate a significant amount of heat during their operation. This is particularly true for electromechanical rotary machines in aircraft applications, which rotate at high speeds of up to 200,000 RPM or more. This heat generation comes from two major sources, electrical losses and friction losses. At very high rotation speeds, friction losses become dominant. These losses cause reduced machine efficiency, and when dissipated in heat, they result in high temperatures. Speeds can be limited by the temperature capabilities of the materials of construction. Successful high-speed motor or generator designs need to minimize the friction losses, not only to improve machine efficiency, but also to provide for carrying the heat of the friction losses away from the surfaces most affected and thus keep maximum temperatures within the limits of the materials of construction.
Liquid cooling devices have been developed that are arranged around the exterior of the machine housing to remove heat. This liquid cooling device and method may be insufficient at times. However, there is no satisfactory solution in the prior art that may be incorporated. Accordingly, it is necessary to develop a cooling system that removes a greater amount of heat than prior art systems.
Typically a very narrow gap is used between rotors and stators. More recently, an electromechanical rotary machine configuration has been developed that utilizes a wider gap between the rotor and stator in an effort to minimize frictional loses caused by the narrow gap in the prior art. Prior art machines have incorporated internal cooling airflow routed through the machine in a variety of ways, but the narrow gap between the rotor and stator does not permit a cooling airflow sufficient for cooling at high rotational speeds there between.
Another prior art machine applies pressurized air during a start-up procedure to displace any oil in the gap or prevent entry of additional oil into the gap. The prior art indicates that air should not be used in the gap for cooling because pressurized air supplied to the gap at high rotational speeds would produce undesirable friction and heating of the rotor and stator.
Therefore, what is needed is an improved electromechanical rotary machine system that provides improved cooling by the use of airflow to directly remove heat from the rotor and stator surfaces.